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CryoSat’s exceptionally detailed data have been used to generate this map of sea-ice thickness in the Arctic. Data from January and February this year have been used to show the thickness of the ice as it approaches its annual maximum. Thanks to CryoSat’s orbit, ice thickness close to the North Pole can be seen for the first time.

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Bad news for polar bears: sea ice is thinning

Not only is the sea ice in the Arctic becoming thinner, multiyear ice will be largely replaced by seasonal ice, according to a recent Swedish study published in the journal Climate Dynamics.

The ice cover of the Arctic Ocean responds in a very sensitive way to climate change. During the last decades, the summer sea ice thickness and extent have decreased at a worrying rate. This new modelling study by Göran Björk and his PhD student Christian Stranne, University of Gothenburg, Sweden, allows for regional variations in ice types and thickness. The difficulty with modelling the response of sea ice to climatic change lies in the fact that the ice is far from homogeneous. Some areas are broken up in floes of various sizes and shapes.

Their investigations use a sophisticated model tool, 1DICE (developed at the University of Gothenburg). The model is capable of treating many different ice types simultaneously and is fully coupled to the atmosphere and ocean.

Abstract

Submarine and satellite observations show that the Arctic Ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades. Here the response of the Arctic Ocean ice cover to changes in the poleward atmospheric energy transport, F wall, is investigated using coupled atmosphere-ice-ocean column models. Two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness-ice volume export feedback and the positive surface albedo feedback. The steady state ice thickness as a function of F wall is determined for various model setups and defines what we call ice thickness response curves. When a variable surface albedo and snow precipitation is included, a complex response curve appears with two distinct regimes: a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime. The two regimes are separated by a steep transition associated with surface albedo feedback. The associated hysteresis is however small, indicating that the Arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback. The results are discussed in the context of the recent reduction of the Arctic sea ice cover. A new mechanism related to regional and temporal variations of the ice divergence within the Arctic Ocean is presented as an explanation for the observed regional variation of the ice thickness reduction. Our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i.e. large areas of the Arctic Ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness, corresponding to the above mentioned transition, and into a state dominated by seasonal ice.